[ntp:questions] NMEA ref.clock better than my ISP's timeserver?

David Lord snews at lordynet.org
Sat Jun 13 17:03:57 UTC 2009


Unruh wrote:
> David Lord <snews at lordynet.org> writes:

....

>> I'm very happy to give chrony another try. I used it for a few
>> years without problems when on dialup. I'm thinking of
>> notebook rather than servers but I'd be happy to try on one of
>> servers (webserver uses ntpd but has chrony-1.20nb3 which I
>> guess is old).
> 
> Yes, that is old. The latest is 1.23 but 
> Miroslav Lichvar has since then put in a patch for giving chrony an shm
> refclock driver 
> I am not sure if I can post the location of the patch, but his email is mlichvar 
> at redhat dot com
> This is beta software, so report to him if you find bugs.
> It needs a line in chrony.conf
> refclock SHM 1 poll 4 offset 0.0 refid GPS1
>  (poll, offset, refid are optional) The "1" refers to the shm port
> number (gpsd uses 1) 
> 
> Note that he finds that chrony is about a factor 20 better than ntp at
> poll level 4 (I think there is something wrong there) and about 2-3
> times better at poll level 3. I suspect this depends crucially on the
> thermal behaviour of the computer. 

I've installed chrony on an eee-pc running ubuntu but the mobile
broadband connection is worse than useless. Dns seems to go awol
or just doesn't happen. I can access sites by ip but even then
have rtt from 0.5s through 2s. I can also manage 3Mbit/s file
transfers over this high latency link, 50% faster than my 2Mbit/s
wired broadband? Bind now installed but not yet setup and it
doesn't address the latency problem.


I've also installed chrony on ubuntu desktop but guess for this
experiment it's better on one of the NetBSD servers. v1.23 is in
pkgsrc so I'll swap one of servers to that (I've run mixed chronyd
and ntpd before without problem and can always switch back).

cheers

David




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